Weird Code 51 and 52
 

Alrighty, I'm a long time puller from this site, but few and far between poster but I need ya'lls help with this one. My CEL has been on for years, ever since I bought the truck back in high school (88 4Runner 3.0). I never thought much of them as the truck had always run fine; I.e. Idle is 800rpm, a/c works fine, plenty of power (Even for the 3.0) up hills and at 7220 feet up here in Wyoming where I go to school. You can smell from the exhaust that she does run a little rich, but I still average 20+mpg. But now I'm determined now to fix the CEL.

I just crested the 250k mark and thought it was time for some maintinence. Last week (in an apartment complex parking lot no less) I just replaced the timing belt, cap, rotor, water pump, thermostat, upper idler pulley, tensioner pulley, valve cover gaskets, upper and lower intake gaskets and all new 200+ miles of vaccum and cooling hoses all the way around.
While I had the lower intake manifold off I checked out the knock sensor because I knew it was throwing a code. It seemed ok, but the wire going to it was torn up and the insulation was melted. I did as other threads suggested and re-wired it with some heavy insulation wire to minimize noise. After that, everything went back on just fine and after a slight timing adjustment, the truck runs just fine like it used to. But I'm still throwing those two codes. P.S. the TPS was replaced 3 years ago, and MAF was replaced 8 months ago.

Now, here's the weird part. When I start the truck, the CEL is off. It won't come on at idle. In fact, it won't come on during reverse or 1st gear. I could red, line it in 1st gear and it would stay off. But as soon as I shift to 2nd and even slightly engage the clutch, it comes back on. It still is flashing me a 51 and 52. I'm at a loss as to how shifting from 1st to second could do this. There's no mention of this on any of the other code forums I've read through...and I've read through a lot. If you have any tips please throw them at me!

Check out the knock sensor (52) threads. The code comes on at a certain vehicle speed

Once again, I'm sorry to beat a dead horse, but all the 51 and 52 threads make no mention of this. It also does not depend on what speed I am going when I shift.

interesting... even like a rolling 1000 shift?
are you clearing the codes before reporting you see the CEL again?

It's an automatic ? Or stick? I have no experience with code 51. But 52 is a tricky little bug. It can be quite a bit of different things. There is a lot about it in other threads. Starting another wouldn't accomplish much. Just read about it. Code 51 anyone? I have no clue

The pigtail that goes to the knock sensor(the wires you replaced) need to be replaced with a Toyota harness. If you go that far, you should just put a Toyota sensor in it too. Problem solved...... the Toyota harness is like 20 bucks

Yes, even when I reset the CEL, it still throws it at me when I shift from 1st to 2nd and I get a 51 and 52 without fail. I think in order to solve the knock issue Im going to do what this video shows. Pretty ingenious really. Let me know if you think this is a good idea.

That's a really interesting solution for that issue...looks reasonable.

somebody did the S10 knock sensor to mine before i bought it.
the light doesn't come on & doesn't give a code.
although i'm not sure why he had to run an extra piece of wire to do it rather than use the existing wires :/

::::::takes coffee and dumps it on the key board:::::::: another knock sensor thread is born

::::::football spikes the phone to the cement:::::::

Sorry man. I didn't mean to start another huge one. I know theres hundreds out there, I was just curious to get ya'lls take on the correlation of the CEL coming on with the shift to second. I haven't found anything on that. I think (just by pure logic and guessing) that its coming on because when I shift to second, the ECU is getting a funny reading from somewhere in the engine - maybe too rich, maybe too lean - and its tripping the TPS system. I think the knock sensor is just a by product thats been there for years.

Quick question - Did they mount it in the same place as in the video? Right to the engine hoist? I'm trying to think of another place to put it, but that really seems to be about it.

it is right above the middle spark plug.
a socket/extension bumps on it while removing the spark plug.

No big deal. I battled a similar issue on my truck. I can't stress it enough. The only good way to repair this is with Toyota parts. Others somehow......have have luck with a doing it other ways. Fallow the other threads to test the wires that talk to the ecu. Check the connection at the harness. The pigtail that runs under the head needs to be Toyota....the knock sensor needs to be Toyota. The ground wire must be shielded. Anything other than this will just cause check engine lights